Autophagy is important in cancer development, progression and response to therapy. Although we are already trying to target autophagy in the clinic, there is currently no way to identify the tumors that will or will not benefit from autophay inhibition and it is unknown if tumors that are driven by different oncogenic driver mutations will differ in their response to autophagy inhibition or not. Because different tumor drivers have opposing effects on autophagy (e.g. mutant RAS is thought to promote autophagy while loss of PTEN activates the canonical PIK3C pathway which should inhibit autophagy), it is likely that tumors with different drivers will differ in their autophagy dependency and thus respond differently to autophagy inhibition. In animal models using conventional (albeit state of the art) genetically engineered mouse (GEM) models, accumulating evidence suggests that RAS-driven tumors benefit from autophagy inhibition. However the time and cost associated with making such GEMs makes testing multiple clinically relevant tumor drivers head to head along with multiple autophagy regulators very difficult and expensive. In this pilot project we aim to develop a new approach that will allow us to directly assess the effects of inhibiting autophagy by targeting different autophagy regulators and in tumor cells driven by five different clinically relevant prostate tumor drivers and to do so both in vitro and during cancer development and progression in vivo. We will do this by capitalizing on a novel approach pioneered by the Cramer lab that uses engineered purified prostate stem cells recombined with urogenital mesenchyme to grow tissue recombinants that mimic normal prostate tissue or aggressive tumors driven by specific tumor drivers (RAS activation, PTEN loss etc.). We will combine this new approach with new methods from the Thorburn lab to target and assess autophagy, allowing us to test the effects of inhibiting three essential autophagy regulators that control distinct steps in the autophagy process in tumor cells driven by five different combinations of tumor drivers all associated with aggressive human prostate cancer and predicted to have different and sometimes opposing effects on autophagy. We will perform both in vitro and in vivo analysis to test our central hypothesis: different tumor drivers cause tumor cells to display different degrees of autophagy dependence in vitro and respond to autophagy inhibition in vivo. We will do this with two aims: 1. Determine the effects of specific tumor-driving oncogenic mutations on autophagy and autophagy-dependence in vitro. And 2. Determine the role of autophagy in prostate tumor development & progression in vivo in the context of different oncogenic mutations/drivers. This high risk/ high return project will establish if our approach is feasible o not and thus allow us to know how to proceed with a larger research project to determine the importance and mechanism of these effects and assess whether analysis of tumor mutations can be used to select patients whose cancer is most likely to respond to autophagy inhibition therapy. We believe these characteristics of high risk but potential for high return with the abiliy to identify a clear way forward based on the results obtained makes this project ideal for the R21 mechanism.